U.S. Pat. No. 4,761,226, assigned to the assignee of the present invention, discloses a media filter filtration apparatus having an upper filter tank. The upper tank includes a perforate floor provided with a lower filtrate compartment covered with a filter media. The lower compartment is connected to the intake of a pump. The filter media, either a paper web or a fibrous filter aid, is supplied from a roll of the media and moved downwardly along an end wall of the tank and across the floor where the media is indexed by a conveyor. The filter media is moved and subsequently removed when contaminated by advancing the conveyor after any vacuum is relieved. A take-up mechanism is operated in connection with the indexing of the media to take-up the contaminated filter media.
In this arrangement, the take-up mechanism utilizes a pneumatic motor to turn a shaft around which contaminated filter media is rewound. This motor is a constant torque device and as such its use results in varying tension on the contaminated filter media as the spent roll changes in diameter. This often results in the filter media being stretched excessively and the edges of the filter media being pulled toward the center when the spent roll is small causing chip migration. In addition, the pneumatic drive requires a complex system of regulators, oilers, valves and piping that is difficult to maintain and keep running.